Vibrational and theoretical analysis of the protonation of 3,4'-bi-1,2,,4-triazole and its C-bromo and C-methyl derivatives

An approach to determine the structure of protonated 3,4 ' -di-1,2,4-triazo les was carried out using the semi-empirical M.N.D.O. (modified neglect of diatomic overlap)method. ne results obtained for 3,4 ' -di-1,2,4-triazole s how that the isolated state of the NH form has great stability, and lead to the conclusion that its protonation mainly occurs on one of the pyridine n itrogen of the 4-triazolyle group. The vibration spectra of the di-1,2,4-triazolium, 5-methyl di-1,2,4-triazol ium and 5-bromo di-1,2,4-triazolium chlorides were studied between 4000 and 200 cm(-1). An attribution of the fundamental modes is proposed, and the e ffect of protonation on the normal vibration frequencies is discussed. Usin g these spectroscopic results, the strength and type of hydrogen bonds exis ting in the crystal could be assessed and a molecular structure proposed.